Histopathological changes in acute ischemic stroke

Romanian Journal of Morphology and Embryology 2009, 50(3):327–339
ORIGINAL PAPER
Histopathological changes in acute ischemic
stroke
OTILIA MĂRGĂRITESCU1), L. MOGOANTĂ2), IONICA PIRICI3), D. PIRICI2),
DANIELA CERNEA4), CL. MĂRGĂRITESCU5)
1)
Department of Neurosurgery,
Emergency County Hospital, Craiova
2)
3)
4)
Department of Histology
Department of Neurology
Department of Anesthesia and Intensive Care
5)
Department of Pathology
University of Medicine and Pharmacy of Craiova
Abstract
We study here the histopathological changes in twenty-two cases of acute ischemic stroke. The average age of the patients was 62-yearold, and the interval from the onset of the disease to the death varied from 6 hours to 15 years. The brain lesions after acute stroke were
observed in all regions. Their evolution allowed us to classify them in fourth stages. Phase one changes (1–2 days after onset) (n=2
patients) included red hypoxic and “ghost” neurons and other acute neuronal injury and spongiosis. The second phase (n=14 patients) was
subdivided into: (a) a phase of acute inflammation (3–37 days after onset) (n=5 patients), where we observed especially features of acute
inflammation together with coagulative necrosis, and (b) phase of chronic inflammation (10 days–53 years after the onset) (n=9 patients),
in which prevail mononuclear and macrophage infiltrate, astrogliosis, spongiosis and neo-vascularization. In the third phase (26 days–
23 years after the onset), we included six cases characterized by the absence of an inflammatory reaction, presence of cavitation,
astrogliosis and macrophages. Our study describes the heterogeneity of brain injury after acute ischemic stroke with the participation of all
brain components, and the chronology in which these lesions develop and evolve.
Keywords: brain, infarct, histopathology, stroke.
Introduction
Stroke, previously called cerebrovascular accident
(CVA) is characterized by the sudden loss of blood
circulation in an area of the brain, resulting in a
corresponding loss of neurological function.
In USA, incidence for first-time stroke is more than
700.000 per year, of which 20% of the patients will die
within the first year after the onset of the stroke.
Keeping the current trends, this number is projected to
rise up to 1 million per year by the year 2050 [1].
Worldwide, in 1990, cerebrovascular disease was the
second leading cause of death, killing more than
4.3 million people [2], and also was the fifth leading
cause of occupational impairment [3]. Although stroke
often is considered a disease of the elderly, one third of
strokes occur in persons younger than 65 years, men
being at higher risk for stroke than women [1].
Strokes are broadly classified as either hemorrhagic
or ischemic. In the last years, a great deal of efforts was
directed toward understanding the pathophysiology and
histopathology of cerebral infarcts, in both humans and
experimental animal models [1, 4–21].
The aim of our study was to investigate the
morphological changes in cerebral parenchyma after
acute ischemic stroke, attempting to establish the
cellular sequential steps that define this pathology.
Material and Methods
Twenty-two cases of acute cerebral ischemic stroke
were selected from the archive of Pathology Department
from Emergency County Hospital, Craiova, Romania,
over a period of 20 years (1987–2006).
Medical records were reviewed to retrieve information regarding patient age at the time of death or
surgery, gender, signs and symptoms at presentation,
radiological characteristics of the lesions, duration of
survival from the date of admission until death or
surgery, and the cause of death. Information obtained
from the autopsy protocol included lesion location,
size, distribution within a particular arterial territory,
macroscopic characteristics, status of intracranial arteries
and general autopsy findings.
The histological specimens were collected during
necropsy and were process in routine histopathological
techniques (10% buffered neutral formalin fixation,
paraffin embedding, 3–5 µm thick-section cutting), and
stained by Hematoxylin–Eosin, Cresyl Violet, Mallory’s
trichrome, and Luxol Fast Blue–Periodic Acid-Schiff–
Toluidine Blue stains.
Macrophages, astrocytes and lymphocytes involved
in cerebral infarction were studied by immunohistochemistry using “ABC”-peroxidase technique (with
VECTASTAIN Elite ABC Kit, Vector Laboratories,
Otilia Mărgăritescu et al.
328
PK-6200, Medikalkit, Craiova, Romania), and CD68
(Monoclonal Mouse Anti-Human, Clone: KP1, Dako,
M0814 Medikalkit), GFAP (Polyclonal Rabbit AntiGlial Fibrillary Acidic Protein, Dako, Z0334,
Medikalkit), CD3 (Polyclonal Rabbit Anti-Human,
Dako, M7254, Medikalkit) and CD20cy (Monoclonal
Mouse Anti-Human, Clone: L26, Dako, M0755,
Medikalkit), according to the manufacturer protocol.
First, we investigated and characterized the
morphological and histopathological changes observed
in the collected specimens, and second we grouped
them according to Mena H et al. in three chronological
phases [1]: (I) phase of acute neuronal injury (1–2 days
after onset), (II) phase of organization, subdivided
into an acute and chronic phase, according to the
nature of the inflammatory infiltrate, and the final
(III) stage – the resolution phase, which starts as early
as 26 days.
Results
Considering the gender repartition, the 22 patients
studied were grouped as 68.2% men (n=15) and 31.8%
women (n=7). The average age at onset was 62 years;
range 27–91 years.
The autopsy protocol revealed that 21 patients
developed the lesions in the cerebral hemispheres
and only one case exhibited affected basal ganglia.
In 17 cases, we were able to establish the affected
vascular territory: left middle cerebral artery (n=8), right
middle cerebral artery (n=6), left internal carotid artery
(n=1), right internal carotid artery (n=1), and left
anterior cerebral artery (n=1). All infarcts represented
isolated lesions. The evolution time of these strokes
varied from 6 hours to 15 years (determined by
measuring the time elapsed between initial clinical
presentation and date of death).
The results of the histopathological evaluation
are shown in Table 1.
Table 1 – Histopathological changes in human acute
ischemic stroke (n=22)
Histopathological changes
Eosinophilic (red) neurons
Other acute neuronal injuries
Coagulative necrosis
Cavitation
Astrogliosis (gemistocytes)
Spongiosis of surrounding tissue
Neo-vascularization
Hemorrhage with intact
erythrocytes
Hemosiderin pigment
Vascular thrombosis
Polymorphonuclear leukocytes
Mononuclear inflammatory cells
Macrophages
Time
n (%)
1–35 days
39 (28)
1–60 days
68 (50)
1 day–5 years
82 (60)
12 days and older 10 (45)
2 days and older 114 (83)
1 day and older
20 (90)
3 days and older 15 (68)
6 (27)
3 days and older
1–37 days
3 days–53 years
3 days–53 years
10 (45)
4 (18)
4 (20)
9 (41)
16 (72)
Cerebral parenchyma alterations in acute
ischemic stroke
Neuronal injury during acute ischemic stroke
Neuronal mitochondrial metabolism dysfunction
(translated as red, eosinophilic neurons) appears in the
earliest phase of infarction. Eosinophilic neurons can
persist in the ischemic penumbra for many months
(2–6 months).
The earliest neuronal injury consisted in increasing
cytoplasm eosinophilia (Figure 1a), with the nucleus
appearing shrunken and darkly basophilic (Figure 1b),
or developing clumped chromatin condensations. In the
later stages, the cytoplasm was uniformly structureless,
and the nucleus showed advanced degeneration and
appeared homogeneous. Finally, the neurons are disintegrated resulting eosinophilic debris. The neuronal
debris were dispersed throughout the neuropil and
scattered eccentrically from the remainder of the dead
neurons. Later on, all these remains were phagocytized
by macrophages (also called “foamy” macrophages in
respect to their fine vacuolated cytoplasm that
accumulates myelin debris).
Other noticed neuronal changes consisted in:
vacuolation of the cytoplasm, shrinkage, or loss of their
affinity for Hematoxylin („ghost neurons”). In the
penumbra, we observed eosinophilic ischemic neurons
spread in a disseminated fashion among the normallooking neurons, and were surrounded by an increased
numbers of oligodendrocytes (satelitosis) (Figure 1c).
Some of these eosinophilic cell bodies were remarkably
shrunken with condensed and clumped nuclear
chromatin and surrounded by swollen astrocytes.
These aspects were present in cerebral infarcts, ranging
in age from 1 day to 2 months. The axonal changes
consisted in fragmentation and degenerative changes
of myelin tracts in white matter (Figure 1, d and e).
Microglial response to acute ischemic stroke
First, resting microglia become rod-shaped and they
were distributed along the capillaries, in the neuropil,
and sometimes capping the surviving neurons. Around
dying neurons the microglial cells retract their processes
and assume an amoeboid morphology, becoming
activated (Figure 1f).
In few samples, we observed signs of phagocytosis
of the dying neurons. After 24 hours from the onset,
in the penumbra, the microglial reaction is well
developed.
Astrocyte response to acute ischemic stroke
In the area of infarct itself, astrocytes had necrotic
aspects (Figure 2a), while in the penumbra they were
viable and became reactive in the periphery of this
region (reactive astrocytosis) (Figure 2b).
The earliest observed modification in response to
cerebral anoxia was astrocyte swelling with watery
cytoplasm, initially around capillaries and after
those surrounding necrotic neurons. In those infarct
lesions older than 2 weeks they become gemistocytic
astrocytes, presenting a large cytoplasmic mass,
long, branching processes, and large and clear nuclei
(Figure 2, c and d).
In the final stages of necrosis the whole parenchyma
was invariably liquefied (Figure 2e), resulting in
eosinophilic cellular debris.
Cavitation by massive coagulative necrosis was
Histopathological changes in acute ischemic stroke
observed in 10 cases (45%). These were present after
two weeks from the onset of the stroke, and usually
were filled with necrotic material accompanied by
inflammation, macrophages and neo-vascularization.
Only in two cases, we noticed cavitated infarcts that
were empty or contained strands of glial fibrillary
processes. Usually, the parenchyma near the borders of
the cavity contained a belt of limiting reactive
astrogliosis.
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Vascular changes in acute ischemic stroke
The earliest vascular modifications in the
infracted area consisted in swelling of the capillaries
endothelium and invagination of the endothelial
nuclei into the vessel lumen. Also, we observed
irregularities in the capillary lumen, hyalination
(Figure 2f) and sclerosis of arterioles within the white
matter.
Figure 1 – Cerebral parenchyma alterations in acute ischemic stroke: (a) “red” neurons and sateliosis, HE staining,
bars; (b) hypoxic neurons with pyknotic nucleus, HE staining, bars; (c) hypoxic neurons surrounded by
oligodendrocytes (sateliosis), HE staining, bars; (d) normal aspect in longitudinal section of the white mater,
Luxol Fast Blue staining, bars; (e) axonal fragmentation, Luxol Fast Blue staining, bars; (f) activated microglia,
CD68 (brown), staining. Bars represent 50 µm.
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Otilia Mărgăritescu et al.
Figure 2 – Cerebral vascular and parenchyma alterations in acute ischemic stroke: (a) necrotic astrocytes,
GFAP (brown) staining, bars; (b) reactive astrocytes, GFAP (brown) staining, bars; (c, d) gemistocytic astrocytes,
HE staining and GFAP (brown) staining, bars; (e) liquefaction zones of cerebral acute ischemic stroke;
(f) hyalinization of cerebral blood vessels from infracted areas, Luxol Fast Blue–PAS staining. Bars represent 50 µm.
Secondary to plasma components extravasation in
the area of the cerebral ischemic stroke, we noticed wall
thickening, cellular infiltration, disintegration and perivascular edema (Figure 3, a and b). This vasogenic
edema was more pronounced in the white matter.
Linking to plasma leakage into the adjacent brain,
we observed the development of spongiosis. This lesion
was present in more than 20 cases (90%) of acute
ischemic stroke at one day or older, both in the gray and
white matter (Figure 3, c and d). Spongiosis of the
neuropil was more constant and prominent and its
intensity decreased with the increase in distance from
the liquefaction zones.
Moreover as a result of blood vessels’ walls anomalies, in less than six cases (27%) we noticed the development of secondary hemorrhages with intact erythrocytes (Figure 3, e and f), and in about 10 cases (45%)
we were able to identify hemosiderin pigment in macrophages and astrocytes adjacent to altered capillaries.
Neo-vascularization was seen in 15 cases (68%),
starting with the day three (Figure 4a). This angiogenesis were more conspicuous at the periphery of the
infarcts, but also was observed in the cavitation zones
associated with inflammation and necrosis.
Only in three cases, we noticed recently thrombosis
of small arteries adjacent to necrotic zones (Figure 4b).
Histopathological changes in acute ischemic stroke
Altogether, we were able to describe the vascular
causes of the acute ischemic stroke in only a few cases
(four cases), thrombosis being observed as a complication of atherosclerosis of the main brain arteries.
Inflammatory reaction in acute ischemic
stroke
The earliest inflammatory reaction observed was the
leukocytes margination in the brain capillaries from the
infarct zone and in meninges onset at 4–6 hours after
ischemia. Less then 20% of acute ischemic stroke
developed a polymorphonuclear leukocyte infiltrate, this
331
reaction being more obvious after 6 day. From 72 hours
until two months, we noticed the presence of a
mononuclear inflammatory infiltrate (Figure 4, c and d).
Between day 7 and 14th, the macrophage response was
maximal, as they became engorged with a foamy material
(Figure 4e). Macrophages were present in 16 (72%)
infarcts from 3 days to 53 years after the onset. In four
cases, we could not establish the presence of inflammatory mononuclear cells and macrophages. By immunohistochemistry, we observed that the majority of the
lymphocytic infiltrate consisted of T-cells (Figure 4f).
Figure 3 – Cerebral vascular changes in acute ischemic stroke: (a) cerebral subleptomeningeal edema, HE staining,
bars; (b) perivascular edema in the infracted zone, HE staining, bars; (c, d) neuropil spongiosis, HE staining, bars;
(e, f) secondary hemorrhages in the infracted area. Bars represent 50 µm.
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Otilia Mărgăritescu et al.
Figure 4 – Cerebral vascular and inflammatory changes in acute ischemic stroke: (a) neovascularization in the
vicinity of infracted area, HE staining, bars; (b) thrombosis of a small artery adjacent to necrotic zone, HE staining,
bars; (c) vessel from the penumbra zone with mononuclear inflammatory infiltrate, CD31 (brown) staining, bars;
(d) macrophages infiltration surrounding a blood vessel from the penumbra zone, CD68 (brown) staining, bars;
(e) foamy macrophages in the infracted area, HE staining, bars; (f) predominant T-cells lymphocytic infiltrate,
CD3 (brown) staining. Bars represent 50 µm.
Histopathological classification of acute
ischemic stroke
According to the Mena H et al., the histopathological
findings in our casuistry of acute ischemic stroke were
grouped as described in Table 2 [1].
For the acute neuronal injury phase we had only two
cases from our casuistry and these were histopathologically characterized by the presence of neuronal
changes, especially eosinophilic and ghost neurons,
by the presence of coagulative necrosis, spongiosis in
gray matter (most probable due to cytotoxic edema),
and in half of the cases by a neutrophilic infiltrate.
In the organization phase, we described 14 cases that
represented 64% of our casuistry. Five cases, ranging in
infarct age from 3 days to 37 days presented histopathological changes typical for acute inflammation.
So, these cases were characterized by the presence of
coagulative necrosis, spongiosis (both in gray and white
Histopathological changes in acute ischemic stroke
matter and due to cytotoxic and vasogenic edema)
and by a polymorphonuclear leukocyte infiltrate.
Other histopathological changes presented in a small
proportion were: acute neuronal injuries, astrogliosis,
neo-vascularization and mononuclear and macrophages
infiltrate. We included nine cases (41%) in the
chronic inflammatory sub-phase of organization, and
they were characterized by lacking acute inflammation
333
and by the presence of mononuclear and macrophage
infiltrate, astrogliosis, spongiosis and neo-vascularization.
In the third phase, we included six cases. They
ranged in infarct age from 26 days to 23 years, and
were characterized by the absence of an inflammatory
reaction, presence of cavitation, astrogliosis and macrophages.
Table 2 – Classification of the histopathological changes in our casuistry of acute ischemic stroke, according to
Mena H et al. (2004)
Histopathological changes
Acute neuronal
injury
n=2, duration
1–2 days
+cases
%
Eosinophilic (red) neurons
Other acute neuronal injuries
Coagulative necrosis
Cavitation
Astrogliosis (gemistocytes)
Spongiosis of surrounding tissue
Neo-vascularization
Polymorphonuclear leukocytes
Mononuclear inflammatory cells
Macrophages
2
2
2
0
0
2
0
1
0
0
100
100
100
100
50
0
0
Phase
Phase of organization
Chronic
Acute inflammation
inflammation
n=5, duration
n=9, duration
3–37 days
10 days–53 years
+cases
%
+cases
%
3
4
5
0
3
4
2
4
2
3
Discussion
Cerebral parenchyma alterations in acute
ischemic stroke
As we described, the first morphological modification
in ischemic cerebral stroke was neuronal injury,
especially the neuronal death. Such neurons appeared
first in the centre of ischemic stroke and they were
coagulative necrotic neurons and few later on were
observed in the penumbra zone as necrotic or apoptotic
cells.
Numerous studies revealed that neuronal death
could occur by one of the three major mechanisms:
apoptosis, autophagia and coagulative necrosis; neurons
having the potential for exhibiting all modes of death in
response to an ischemic insult [22–24]. Apparition of
one these modes of cell death depends of the nature of
the insult, the cell type, age, and very probably of
the state of the cell at the time of the insult [25].
Additionally to its multimodal nature, ischemic
neuronal death is also characterized by a long delay
between the insult and manifestation of major cell
damage, from few hours or less [26] to several days or
even weeks [27, 28], depending on the nature of the
insult and the brain region being affected [22].
Morphologically, were described three categories of
necrotic death neurons:
▪ Edematous or pale neurons. Such neurons had very
swollen cytoplasm (with some swollen and disrupted
mitochondrial cristae, remnants of Golgi apparatus with
attached ribosomes accumulated near the nucleus),
an irregular plasma membrane or very rare with
clear breaks, irregular clumping of chromatin [29–31].
Such neurons are very rarely seen, they predominate
60
80
100
0
60
80
40
80
40
60
2
4
7
2
8
9
8
0
7
9
22
44
77
22
88
100
88
0
77
100
Resolution phase
n=6, duration
26 days–23 years
+cases
%
0
1
2
4
6
5
2
0
0
4
0
17
33
67
100
83
33
0
0
67
after 3- to 4-hours of hypobaric/ischemia in young
animals [32], a state that can also be produced by
glutamate exposure [32–34].
▪ Ischemic neuron change („eosinophilic” neurons).
It is the most common modification that dominates in
CA4 after global ischemia in gerbil [35] and rat [36].
These neurons are abundant in the penumbra for
1–2 days and in the core of the lesion for a relative short
time before the cells disintegrates [22]. These cells
are intensely acidophilic (eosinophilic), often with
triangular shape, major darkening and shrinkage of
the nucleus and cytoplasm [30, 36] and a honeycomb
appearance of the nucleus [37].
▪ „Ghost” neurons. These cells are weakly
eosinophilic, with a somewhat shrunken and slightly
darker nucleus than normal, often with a fragmented
membrane and irregular chromatin clumping. The cytoplasm is slightly shrunken and appears fragmented with
small vesicles and dense bodies [8, 38, 39], but still
retains its delimited structure. Such neurons appeared at
24 hours after anoxia/ischemia [38], and 6–12 hours
into permanent focal ischemia in rat, in the core of the
lesion [39], and sometime before 48 hours after 2-hours
focal ischemia in the penumbra [40].
Experimental ischemia and reperfusion models,
such as transient focal/global ischemia in rodents,
have been thoroughly studied and the cumulative
evidence suggests the involvement of cell survival/death
signaling pathways in the pathogenesis of apoptotic
cell death in the ischemic lesions [24, 41–44].
Morphological evidence for apoptosis is weak, the
apoptotic bodies probably have a short lifetime
(approximate 3 hours), and it has been suggested that
this might explain their absence.
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Otilia Mărgăritescu et al.
The existence of neuronophagia in ischemic
condition is not very well established [45, 46]. These
neurons had a condensed cytoplasm containing many
large vacuoles, most of which are autophagosomes or
proliferating lysosomes, and a nucleus in which
chromatin is irregularly clumped, less pynknotic and
less dense than in coagulative necrosis.
It has been reasoned that dead neurons and
ischemically injured tissue are scavenged by activated
resident microglia and/or macrophages that have
invaded into the injured tissue from the blood stream
[47, 48]. However, Ito U et al. found a novel scavenger
mechanism in the ischemic penumbra, one by which
dead neurons were fragmented by invading small
astrocytic processes and only a thinned-out core portion
remained, which finally became a tiny vesicular
particle. The dispersed fragmented pieces were
phagocytized by the microglia and astrocytes late,
at 8 to 24 weeks postischemia [49].
In our study, beside neuronal damage other nonneuronal cell population injuries consisted in coagulative necrosis of the microglias, oligodendroglias and
astrocytes in the core of the ischemic cerebral infarcts
and proliferation and activation of such cells in the
penumbra zone.
Studies on cerebral ischemia proved that microglial
response occurs gradually. First, microglias proliferate
and become activated; and second, they are transformed
into intrinsic brain phagocytes [47, 50, 51]. Moreover,
after ischemic injury, the ramified morphology of
resting microglia is transformed into a hyper-ramified
intermediate form [52] before transforming into
“reactive microglia” [53, 54]. However, at the site of
ischemic damage, microglial proliferation and activation
has been reported to occur rapidly within the first
24 hours after an ischemic insult [53, 55, 56]. Within
the infarct, the phagocytes with a foamy cell appearance
and derived from local resting microglia and/or from
the bloodstream, are abundant within a few days [57].
In the study of Ito U et al. it was demonstrated that
in the ischemic penumbra microglial proliferation
and activation occurred gradually from 1 to 12 weeks
after the transient ischemic insult, and phagocytic
microglia were first prominent at 8 to 12 weeks [49].
Also, it seems that the increased number of activated
microglia after ischemic injury not only precede but
is a likely cause of astrocytic hypertrophy (reactive
astrogliosis [58, 59].
Garcia JH et al. and Petito CK et al. had shown
that astrocyte swelling is a prominent as well as the
earliest response in cerebral anoxia-ischemia [60, 61].
Panickar KS and Norenberg MD proved that astrocyte
swelling occurs initially in end-feet around capillaries
eventually the entire cell becomes swollen. In addition
to swelling, astrocytes show slight cytoplasmic
hypertrophy as early as 1–3 hours post-ischemia [61];
the cytoplasm contains increased numbers of mitochondria and rough endoplasmic reticulum in keeping
with evidence of increased protein synthesis [62].
The nuclei of these astrocytes are enlarged and pale.
Such astrocytes resemble to Alzheimer type II astrocytes
that have been described in hyperammonemia and
hepatic encephalopathy [63]. Most probable these cells
represent an early phase in the process of transformation
to the reactive astrocyte [64]. In the penumbra zone,
the surviving astrocytes undergo a process of hypertrophy, and to a lesser extent proliferation referred to
as reactive [65]. At two weeks of the ischemic injury,
they enlarge the cytoplasm (gemistocytic astrocytes),
being generated new, thicker, and longer cytoplasmic
processes. In addition, were observed other morphological changes typical for metabolically activated
astrocytes such as: increase of the nuclear size, irregular
nuclear outlines along with dispersion of chromatin,
increased numbers of mitochondria and ribosomes, and
enlarged Golgi complexes [64]. As an attempting to
restore the composition of the external environment and
to stimulating reparative processes the gemistocytic
astrocytes by their cytoplasmic processes create a
meshwork around the area of necrosis forming the socalled “glial scar” [65].
Generally, it is believe that the surviving astrocytes
in the penumbra region of cerebral infarct may facilitate
restoring neuronal integrity by producing growth factors,
cytokines, and extracellular matrix molecules, involved
in repair and regenerative neuronal mechanisms [64].
It is well known that astrocytes are more resistant
than neurons to anoxic-ischemic injury, but there is also
a differential sensitivity among astrocytes from different
brain regions. Thus, was demonstrated that hippocampal
astrocytes from rats and mice are more vulnerable than
cortical astrocytes after oxygen-glucose deprivation
[66, 67]. Also, Lukaszevicz AC et al. showed that after
permanent occlusion of the middle cerebral artery in
mice, fibrous astrocytes located at the brain surface
displayed a transient and limited hypertrophy, with no
conspicuous cell death, whereas cortical protoplasmic
astrocytes were more vulnerable [68].
Ito U et al. proved that in postischemic conditions,
the number of dead neurons increased in parallel with a
decrease in the numbers of normal-appearing astrocytic
processes (APs) and their mitochondria in the neuropil
[69]. Also, they established that the numbers of normalappearing APs and their mitochondria decreased, and
the number of swollen degenerated ones increased,
around the degenerated and dead neurons.
Pantoni L et al. reported the existence of selective
oligodendrocyte damage in the rat cerebral white
matter after middle cerebral artery (MCA) occlusion
[18]. Therefore, oligodendrocyte swelling occurred
as early as 30 minutes after MCA occlusion, and
pyknosis of these cells was widespread after 6 hours.
The oligodendroglial injury involves a large proportion
of these cells at a time when neuronal damage is
evolving and before infarction (pannecrosis) develops,
suggesting that a number of glial cells may succumb to
the effects of ischemia before morphological
expressions of neuronal death become apparent [18].
The same authors described nerve fiber injury after
middle cerebral artery (MCA) occlusion, consisting in
axonal swelling with dissolution of the cytoskeleton and
periaxonal intramyelinic edema. The authors concluded
that these nerve fiber injuries that occur in the white
matter after MCA occlusion are the direct effect of
Histopathological changes in acute ischemic stroke
335
hypoxic-ischemic injury and are probably independent
of the injury to the neuronal perikarya. Moreover, in
another study it was established that Wallerian
degeneration is a phenomenon that in the central
nervous system occurs only several weeks after the
neuronal perikarya are destroyed [70].
density in the ischemic border indeed correlates with
longer survival in stroke patients [83].
Nevertheless, it seems that these new born vessels
are often abnormally leaky, which might exacerbate
brain edema, a major and often life-threatening
complication of various brain injuries [87, 88].
Vascular reaction in acute ischemic stroke
Inflammatory reaction in acute ischemic
stroke
In our study, we noticed the presence of injured
brain capillaries both inside and outside of necrotic
areas were. First, this alteration consists in blood brain
barrier injury and as a result it develops the vasogenic
cerebral edema. In connection with this, appears the
spongiosis of gray and white matter. As the infarct
progresses, the brain capillary lesions inside the necrotic
area worsen, finally being disintegrated. Simultaneously
adjacent to necrotic areas and in the penumbra zones
begins the neo-vascularization. As results of abnormally
leakage of these new blood capillaries, the brain edema
might exacerbate and also they could be the source for
the secondary hemorrhagic strokes.
In time many studies established that the primary
event could be alteration of cerebral microvascular
endothelial function [71], with extravasation of plasma
components into the arteriolar wall (causing the
wall thickening, cellular infiltration, disintegration,
perivascular damage observed pathologically) [72], and
then leakage into the adjacent brain causing “perivascular
edema-related lesions” [73, 74]. This observation is
supported by the systemic [75, 76] and cerebral [77]
endothelial dysfunction found in lacunar stroke.
Moreover, experimental studies proved that brain
capillary injuries were capable to increased perfusion
deficits in the ischemic penumbra leading to extension
of the infarction [78, 79].
Though the vascular system of the adult brain is
extremely stable under normal baseline conditions,
endothelial cells start to proliferate in response to brain
ischemia.
Experimental studies on transient or permanent
occlusion of the middle cerebral artery demonstrated
that endothelial cells surrounding the infarcted brain
area start to proliferate as early as 12–24 hours
following vessel [80–82]. As a result, the vessels from
peri-infarcted region increase in number at 3 days
following the ischemic injury. The human brain studies
proved that active angiogenesis takes place at 3–4 days
following the ischemic insult [83]. It is not clear for
how long angiogenesis actively occurs in the injured
brain since long-term studies have not been performed
yet. However, Hayashi T et al. described that vessel
proliferation continued more than 21 days following
experimental cerebral ischemia [81].
Additionally, the generation of new blood vessels
facilitates highly coupled neurorestorative processes
including neurogenesis and synaptogenesis, which in
turn lead to improved functional recovery. Thus, it was
proved that the newly generated neurons [84] and
neuroblasts concentrated around blood vessels following
stroke [85]. So, we can conclude that neurogenesis
and angiogenesis might be mechanistically linked [86].
In this idea, it was proved that greater microvessel
Our study revealed that first occur a transient
inflammatory reaction, especially around blood vessels
and in the meninges, in which the prevalent
inflammatory cells were the neutrophils. About 3 day
after ischemia, monocytes from the blood stream enter
the infarct zone through damaged vessels. They ingest
the products of degradation of neurons and myelin and
are transformed into lipid-laden macrophages.
Animal models of focal ischemia induced by middle
cerebral artery occlusion (MCAO) provide most
evidence for cellular inflammatory responses in stroke.
Permanent MCAO results in a modest neutrophil
infiltration at 24 hours after ischemia, predominantly
around arterial vessels at the margins of infarction,
whereas MCAO with subsequent reperfusion is
associated with substantial infiltration by neutrophils
throughout the entire infarct [89]. Neutrophil
accumulation in small vessels including capillaries in
the peri-infarct region may contribute to the ‘no reflow’
phenomenon – a failure of tissue to reperfuse despite
recanalization of the main vessel occluded [90]. Studies
conducted on human suggested an early neutrophil
infiltration from day 1, peaking at days 2–3, and later
monocyte infiltration around day 5 [91, 92].
As we also showed here, recently it was proposed
that as a result of blood–brain barrier breakdown after
stroke, a specific T-lymphocyte mediated immune
response develops [93]. This hypothesis is also
supported by the finding of circulating brain antigenspecific antibodies after human stroke [94], which
triggers the immune response. In animal models of
stroke, this immune response appears to worsen the
outcome [95].
Overall, activated microglia and infiltrating
inflammatory cells secrete proinflammatory mediators
that amplify the inflammatory response, as well as
various effector molecules (proteases, prostaglandins
and reactive oxygen species such as nitric oxide via
inducible nitric oxide synthase), which can directly
damage cells, vasculature or extracellular matrix.
Histopathological classification of acute
ischemic stroke
According to Mena H et al., for cerebral infarcts
classification on morphologic criteria the most encountered cases in our casuistry was at the moment of
pathological diagnosis in organization phase (63%) [1].
The second place was occupied by those cases framed
in the resolution phase (27%) and in the last position
were placed the cases from acute neuronal injury phase
(10%).
Human and experimental studies on histopathological findings in acute ischemic stroke reveled that
336
Otilia Mărgăritescu et al.
neuronal injury, including cytoplasmic eosinophilia and
vacuolation, shrinkage and ghost cells, is identified
within the 1st day of evolution of a cerebral infarct
and that such changes may persist up to 16 days in
the squirrel monkey and 35–60 days in humans [1, 4–7,
9–11, 13–21, 35, 96–102].
Other neuronal injury, including apoptotic bodies are
present from day 1, but neuronal ferrugination take
place after 3 to 10 days. In human brain tissue, necrosis
may be seen as early as 1 day and in the rat after 2 days.
The cavitation usually begins at 12 days in human cerebral infarcts. Astrocytes begin to proliferate at 2 days in
humans and 7 days in the sub-primate brain. The presence of hemosiderin-laden macrophages and hematoidin pigment will be seen after 3 days. Neo-vascularization is seen during the first 24 hours in the rat brain,
at 3 days in humans, and has a delay of 7 days in the
sub-primate brain. In both human and experimental
infarcts acute inflammation started in day 1 and the
polymorphonuclear leukocytes may persist for 7 days in
the sub-primate brain and up to 37 days in humans.
From day 3, the acute inflammatory response will be
gradually replaced by chronic inflammation and macrophages, which may persist up to 53 years.
Chuaqui R et al. defined on human samples four
phases of infarction: initial phase from days 1 to 4,
second phase from days 5 to 7, third from days 8 to 14,
and the last one from days 15 to 27 [4]. In the first
phase, were included red neurons and necrotic oligodendrocytes; the second phase was characterized by the
presence of macrophages and neovascularization, while
in the third were described neuronal ghosts, astrogliosis
and the absence of neutrophils and in the fourth were
absent the of red neurons but was present necrotic
oligodendrocytes and myelin loss at the center of the
infarct. Comparative to Mena H et al. classification,
the Chuaqui R et al. classification had major limitation
owned to absence of discussion about temporal evolution
of the accompanying inflammatory infiltrate, the limited
number of cases and the restricted period of infarct
evolution (no cases exceeded 27 days post-infarct).
Conclusions
Overall, our study proves the heterogeneity of brain
injury after acute ischemic stroke with the participation
of all brain compartments and the existence of a
chronology in developing and evolution of such lesions.
For a complete understanding of acute ischemic stroke
pathogenesis it is absolute necessary to obtained
additional histopathologic data based on human autopsy
and surgical material. This strategy may facilitate the
development of new therapies that could either prevent
or diminish brain injury.
Acknowledgements
This work was supported by the grant PNII/IDEI,
CNCSIS–UEFISCU, ID 2188/2008.
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Corresponding author
Claudiu Mărgăritescu, Associate Professor, MD, PhD, Department of Pathology, Faculty of Dentistry, University of
Medicine and Pharmacy of Craiova, 2–4 Petru Rares Street, 200349 Craiova, Romania; Phone +40740–152 550,
e-mail: c_margaritescu2000@yahoo.com
Received: April 15th, 2009
Accepted: June 25th, 2009